Fe3O4@SiO2@KIT-6@2-ATP@CuI as a catalyst for hydration of benzonitriles and reduction of nitroarenes

In this paper, a new type of magnetic mesoporous material (Fe3O4@SiO2@KIT-6@2-ATP@CuI) was designed and synthesized and its application in the synthesis of amides and anilines was investigated. The structure of Fe3O4@SiO2@KIT-6@2-ATP@CuI was characterized and identified using FTIR, SEM, XRD, TGA, BET, VSM, and ICP techniques. An external magnet can easily remove the synthesized catalyst from the reaction medium, and be reused in several consequence runs.

Scanning electron microscope (SEM) is one of the most common tools used in nanotechnology to analyze the morphology of nanostructural materials. The bombardment of the sample causes electrons to be released from the sample towards the positively charged plate, where these electrons become signals. The movement of the beam on the sample provides a set of signals based on which the microscope can display an image of the sample surface on the computer screen. So, in general, it is possible to obtain information including topography, components, and morphology of the sample 31 .
Thermogravimetric analysis (TGA), using a specific heating program and under a controlled atmosphere, measures weight changes in air or an inert atmosphere and records the mass reduction as a function of increasing     32 . Figure 4 shows the TGA diagram of a catalyst activated with 2-amino thiophenol. According to the diagram, the first weight loss (under 250 °C, about 3%) is related to the evaporation of adsorbed solvents. The second weight loss, which is about 12% and occurred at temperatures between 250 to 650 °C, is related to the removal of immobilized organic compounds, indicating that 2-amino thiophenol was successfully immobilized into KIT-6 magnetic channels.
The X-ray diffraction pattern for the Fe 3 O 4 @SiO 2 @KIT-6@2-ATP@Cu I catalyst is shown in Figs. 5 and 6, (low and wide angle respectively). The low-angle XRD spectrum shows in Fig. 5. In the high-angle XRD spectrum www.nature.com/scientificreports/ ( Fig. 6), the peaks appearing at 43.79°, 50.54°, and 73.24° correspond to the copper metal-stabilized into the channels of the catalyst, and a broad peak of 20-30 is related to the amorph silica layer 33,34 . Figure 7 shows the nitrogen adsorption/desorption isotherm of Fe 3 O 4 @SiO 2 @KIT-6@2-ATP@Cu I . The isothermal adsorption-desorption curve for Fe 3 O 4 @SiO 2 @KIT-6@2-ATP@Cu I shows type IV of IUPAC isotherms, indicating the magnetic material form in a mesoporous structure. The N 2 adsorption-desorption isotherm had a sharp bend at P/P 0 , indicating capillary density in uniform mesopores.
As shown in Fig. 8, the magnetic property of Fe 3 O 4 @SiO 2 @KIT-6@2-ATP@Cu I (1.38 emu/g) shows a significant decrease compared to Fe 3 O 4 @SiO 2 @KIT-6 nanoparticles (3.30 emu/g). The magnetic property of the mesoporous catalyst reflects the fact that the surface of the nanoparticles is coated with SiO 2 and organic groups.
ICP analysis was used to determine the exact amount of loaded Cu on the magnetic mesoporous catalyst and showed a value of 1.11 × 10 -3 mol/g. Catalytic studies. Hydration of benzonitriles to amides. After the structure characterized the magnetic mesoporous catalyst, its catalytic activity in the synthesis of amides was investigated. The reaction of 4-chlorobenzonitrile as model substrate was investigated in the presence of potassium hydroxide, various solvents www.nature.com/scientificreports/ such as water, ethanol, methanol, tetrahydrofuran, and 1-propanol, variable amounts of catalyst, and different temperature conditions. In protic polar solvents, coordination between the solvent and benzonitrile with the catalyst activates the cyano group in the nitrile substrate. Among protic polar solvents, 1-propanol led to more amide formation due to its coordination with the substrate 33,35 . Finally, 1-propanol, 40 mg of catalyst, 70 °C temperature, and 2 mmol of potassium hydroxide were selected as optimal conditions (Table 3). After obtaining the reaction conditions, the reaction of different benzonitriles was performed under optimal conditions and a variety of amides were synthesized (Fig. 9). The results including reaction times and yields are reported in Table 4.
The hydration mechanism in the presence of Fe 3 O 4 @SiO 2 @KIT-6@2-ATP@Cu I is proposed in Fig. 10. Initially, the coordination of benzonitrile with the copper atom from the catalyst may lead to an increase in the   Reduction of nitroarenes to anilines. In another catalytic study, the activity of Fe 3 O 4 @SiO 2 @KIT-6@2-ATP@Cu I in the reduction of nitroarenes to aromatic amines was investigated (Table 5). After considering the effect of different solvents, temperature conditions, and different amounts of catalyst; water as the solvent, and room temperature were selected as the optimal conditions for the preparation of anilines from nitroarenes. The effect of solvent on the reduction of nitroarenes was analyzed through articles and the results show that protic polar solvents are more suitable solvents for the reduction of nitroarenes than aprotic polar solvents 5 .
After obtaining the optimal conditions, the reduction of different derivatives of nitroarenes to aromatic amines was performed and the results can be seen in Table 6 (Fig. 11).
A proposed mechanism for the reduction of nitro compounds in the presence of Fe 3 O 4 @SiO 2 @KIT-6@2-ATP@Cu I is provided in Fig. 12 37 .
Reusability of the catalyst. To investigate the recovery of described catalyst, the reduction reaction of 1-chloro-4-nitrobenzene was selected as the sample reaction. The reaction was selected using 1-chloro-4-nitrobenzene, sodium borohydride, and water as the solvent in the presence of Fe 3 O 4 @SiO 2 @KIT-6@2-ATP@Cu I . After the reaction was complete, it was separated by an external magnetic field, washed with ethanol and water, and then used in the next run. This cycle was repeated up to four times (Fig. 13).

Conclusions
In this paper, the Fe 3 O 4 @SiO 2 @KIT-6@2-ATP@Cu I as a magnetic mesoporous catalyst was designed and synthesized through the combination of Fe 3 O 4 and KIT-6 nanoparticles. The catalytic ability of this mesoporous magnetic material was studied for the preparation of benzamides and anilines. The reported procedure in this research project offers the advantages of reasonable yields and green reaction medium, versatile catalyst preparation procedure, short reaction times of catalytic reactions, easy separation (it could be easily separated and recovered due to its magnetic properties), catalyst recyclability, and high catalyst chemical stability.
In Table 7, the Fe 3 O 4 @SiO 2 @KIT-6@2-ATP@Cu I magnetic catalyst was compared with other previously reported catalysts for the reduction of nitrobenzene. As is evidenced in this table, the obtained results by the described catalyst in this research are comparable with other reductive systems.

Experimental
Synthesis of Fe 3 O 4 @SiO 2 @KIT-6@2-ATP. Fe 3 O 4 @SiO 2 @KIT-6 nanoparticles were synthesized using a method previously reported in the literature 38 . In a 50 mL balloon, Fe 3 O 4 @SiO 2 @KIT-6 (1 g) was sonicated for 30 min in toluene (25 mL), then, 1.5 mL of (3-chloropropyl) trimethoxysilane (CPTMS) was added and the resulting mixture was stirred for 24 h at 90 °C under nitrogen atmosphere. The obtained solid was washed with   The general method for the reduction of nitroarenes to anilines. To prepare anilines from nitroarenes, a mixture of nitroarene, NaBH 4 (5 mmol), and 20 mg catalyst was stirred at room temperature. TLC was used to monitor the progress of the reaction and the product was obtained in high yield after catalyst isolation.  Figure 10. The suggested mechanism of amide synthesis in the presence of Fe 3 O 4 @SiO 2 @KIT-6@2-ATP@Cu I as a catalyst.   Figure 12. A suggested mechanism for the reduction of nitro compounds by NaBH 4 in the presence of a catalytic amount of Fe 3 O 4 @SiO 2 @KIT-6@2-ATP@Cu I .